The present invention relates to a chip type electrophoresis device for analyzing a sample containing an extremely small amount of a protein, nucleic acid, a drug, or the like at a high speed with a high resolution.
In a case that an extremely small amount of a protein or nucleic acid is analyzed, conventionally an electrophoresis has been used, and a capillary electrophoresis has been known as a typical method of the electrophoresis. In the capillary electrophoresis, a matrix for separation (an electrophoresis medium) is charged in a glass capillary (hereinafter simply referred to a capillary) having an inner diameter of 100 μm. A sample is introduced into one end of the capillary, and both ends of the capillary contacts a buffer solution. Then, a high voltage is applied between both ends of the capillary through the buffer solution to thereby develop the sample in the capillary. Since the capillary has a large surface area relative to a volume thereof, that is, the capillary has a high cooling effect, a high voltage can be applied thereto, and an extremely small amount of sample such as DNA (deoxyribonucleic acid) can be analyzed at a high speed with a high resolution.
However, the capillary is easily broken because of a very small outer diameter of about 100 to 500 μm, causing a problem that the capillary is not easy to handle when replacing. Also, there may be a case that the heat radiation may not be sufficient to apply a higher voltage, resulting in a negative effect on a state of sample separation. Further, since the voltage is applied to both ends of the capillary through the buffer solution, the capillary is required to have at least enough length to contact the buffer solution, so that the capillary is required to have a length longer than a certain length.
Therefore, instead of the capillary, there has been proposed an electrophoresis chip formed by bonding two base plates as disclosed in D. J. Harrison et al, Anal. Chem. (1993), 283, 361-366, as a device expected to carry out a high-speed analysis and to reduce a size of the device. An example of the electrophoresis chip is shown in FIGS. 4(A) to 4(C).
An electrophoresis chip 11 is formed of a pair of base plates 11a, 11b having a transparent plate shape formed of an inorganic material. Electrophoresis capillary grooves (channels) 13, 15 crossing each other are formed on a front surface of one base plate 11b, and the other base plate 11a is provided with through holes as a separation buffer waste 17a, a separation buffer reservoir 17c, a sample reservoir 17s, and a loading buffer waste 17w, which are formed at positions corresponding to ends of the channels 13 and 15. The base plates 11a and 11b are laminated and bonded to form the electrophoresis chip 11 as shown in FIG. 4(C).
When the electrophoresis is conducted by using the electrophoresis chip 11, the electrophoresis medium is charged from one of the reservoirs and the wastes to fill the channels 13 and 15, the reservoirs 17c, 17s and the wastes 17a, 17w. Then, the electrophoresis medium in the reservoirs 17c, 17s and the wastes 17a, 17w is removed therefrom. Thereafter, the sample is injected from the sample reservoir 17s corresponding to one end of the relatively shorter channel (a sample introduction flow path) 13, and the buffer solution is injected to the other reservoir 17c and the wastes 17a, 17w. 
After the electrophoresis medium, the sample, and the buffer solution are injected, the electrophoresis chip 11 is attached to an electrophoresis device, and a predetermined voltage is applied to the respective reservoirs 17c, 17s and the wastes 17a, 17w, so that the sample is migrated in the channel 13 to be led to an intersecting portion 19 where the channels 13 and 15 cross each other. Then, the voltage applied to the respective reservoirs 17c, 17s and the wastes 17a, 17w, is switched, and due to the voltage between the reservoir 17c and the waste 17a located at both ends of the relatively longer channel (a separation flow path) 15, the sample in the intersecting portion 19 is migrated into the channel 15. Thereafter, the sample remained in the reservoir 17s is substituted by the buffer solution. Then, the voltage for the electrophoresis is applied to the respective reservoirs 17c, 17s and the wastes 17a, 17w, and the sample injected in the channel 15 is separated therein. By providing a detector at an adequate position on the channel 15, the sample separated by the electrophoresis can be detected.
The reservoirs 17c, 17s and the wastes 17a, 17w are respectively provided with electrodes. These electrodes are in a rod form and may be inserted in the reservoirs and the wastes at the time of analysis, or may be attached thereto by a vapor deposition. Since it is necessary to fill the sample reservoir 17s with an enough amount of the sample to allow the electrode to be soaked sufficiently therein, it is difficult to reduce the amount of the sample.
Further, when the sample contacts the electrode in order to apply the voltage for introducing the sample into the flow path, the electrolysis occurs. If the amount of the sample is small, it is possible that the electrolysis affects the analysis. Therefore, in order to suppress the effect of the electrolysis, it is also necessary that the sample reservoir have a volume more than a predetermined amount. In view of the foregoing, it is also difficult to reduce the amount of the sample.
Accordingly, an object of the invention is to provide a chip type electrophoresis device that can analyze a sample even if an amount of the sample is very small.
Further objects and advantages of the invention will be apparent from the following description of the invention.